My husband was in prison under a alias name. He has no documents stating that as his real name at all. Are we legally married still.

My husband was in prison under his alias name and we got married but he has no documents stating that is his name. Are we legally married.

What is the cheapest way to get divorced. I desperately need help

Yes you are married.

It may have been illegal for him to sign the marriage license using a name not his own, but you have to prove you didn't know (not easy before the court), so you will be advised to just get a divorce. I don't know of a state that has forms for canceling a marriage based on use of an alias.

The cheapest way to get a divorce is to trot down to the County Courthouse and file papers. The easiest way to have papers is to get a copy of someone else's quick divorce and change the names to yours.
There will be a filing fee. When I did it about 20 years ago, it was $100 in that state.
BUT
If hubby isn't in agreement and willing to sign, it gets complicated, and you should look locally for the cheapest lawyer.